1. Field of the Invention
The present invention relates to an apparatus and method for transmitting a protocol data unit in a wireless communication system, and more particularly, to transmitting a protocol data unit having control information and an indicator for indicating the existence of the control information.
2. Description of the Related Art
The universal mobile telecommunications system (UMTS) is a third-generation mobile communications system evolving from the global system for mobile communications system (GSM), which is the European standard. The UMTS is aimed at providing enhanced mobile communications services based on the GSM core network and wideband code-division multiple-access technologies.
A related art UMTS network structure 1 is illustrated in FIG. 1. A mobile terminal 2, or user equipment (UE), is connected to a core network 4 through a UMTS terrestrial radio access network (UTRAN) 6. The UTRAN 6 configures, maintains, and manages a radio access bearer for communications between the UE 2 and the core network 4 to meet end-to-end quality of service requirements.
The UTRAN 6 includes a plurality of radio network subsystems (RNS) 8, each of which comprises one radio network controller (RNC) 10 for a plurality of base stations 12, or “Node Bs.” The RNC 10 connected to a given base station 12 is the controlling RNC for allocating and managing the common resources provided for any number of UEs 2 operating in one cell. One or more cells exist in one Node B. The controlling RNC 10 controls traffic load, cell congestion, and the acceptance of new radio links. Each Node B 12 may receive an uplink signal from a UE 2 and may transmit downlink signals to the UE. Each Node B 12 serves as an access point enabling a UE 2 to connect to the UTRAN 6, while an RNC 10 serves as an access point for connecting the corresponding Node Bs to the core network 4.
Among the radio network subsystems 8 of the UTRAN 6, the serving RNC 10 is the RNC managing dedicated radio resources for the provision of services to a specific UE 2 and is the access point to the core network 4 for data transfer to the specific UE. All other RNCs 10 connected to the UE 2 are drift RNCs, such that there is only one serving RNC connecting the UE to the core network 4 via the UTRAN 6. The drift RNCs 10 facilitate the routing of user data and allocate codes as common resources.
The interface between the UE 2 and the UTRAN 6 is realized through a radio interface protocol established in accordance with radio access network specifications describing a physical layer (L1), a data link layer (L2) and a network layer (L3) described in, for example 3GPP specifications. These layers are based on the lower three layers of an open system interconnection (OSI) model that is a well-known in communications systems. A related art architecture of the radio interface protocol is illustrated in FIG. 2. As shown, the radio interface protocol is divided horizontally into the physical layer, the data link layer, and the network layer, and is divided vertically into a user plane for carrying data traffic such as voice signals and Internet protocol packet transmissions and a control plane for carrying control information for the maintenance and management off the interface.
The physical layer (PHY) provides information transfer service to a higher layer and is linked via transport channels to a medium access control (MAC) layer. Data travels between the MAC layer and the physical layer via a transport channel. Also, data transmission is performed through a physical channel between different physical layers, namely, between physical layers of a sending side (transmitter) and a receiving side (transmitter).
The MAC layer of the second layer provides a service to an upper layer of a radio link control (RLC) layer through a logical channel. The MAC is sub-divided into several types of sub-layers such as a MAC-d sub-layer and a MAC-e sub-layer according to the type of transport channel that is managed.
A related art structure of a dedicated channel (DCH) and an enhanced dedicated channel (E-DCH) is illustrated in FIG. 3. As shown, the DCH 14 and the E-DCH 16 are dedicated transport channels used by one mobile terminal. In particular, the E-DCH 16 is used to transmit data to the UTRAN 6 at a high speed compared to the DCH 14. In order to transmit data at a high speed, various techniques may be employed for the E-DCH 16 such as a HARQ (Hybrid ARQ), an AMC (Adaptive Modulation and Coding), and a Node B controlled scheduling, and the like.
For the E-DCH 16, the Node B 12 transmits downlink control information to a mobile terminal 2 to control the E-DCH transmission of the mobile terminal 2. The downlink control information may include response information (ACK/NACK) for the HARQ, channel quality information (CQI) for the AMC, E-DCH transmission rate information, E-DCH transmission start time and transmission time period information, and a transport block size information for the Node B controlled scheduling, or the like.
Meanwhile, the terminal 2 transmits uplink control information to the Node B 12. The uplink control information may include E-DCH transmission rate request information, UE buffer status information, and UE power status information for the Node B controlled scheduling, or the like. The uplink control information and the downlink control information for the E-DCH 16 are transmitted through a physical control channel such as an E-DPCCH (Enhanced Dedicated Physical Control Channel).
For the E-DCH 16, a MAC-d flow 18 is defined between the MAC-d sublayer 24 and the MAC-e sublayer 26. In this case, a dedicated logical channel is mapped to a MAC-d flow, the MAC-d flow is mapped to the E-DCH 16, a transport channel, and the E-DCH 16 is mapped to an E-DPDCH (Enhanced Dedicated Physical Data Channel) 20, a physical channel. Also, the dedicated logical channel can be directly mapped to the DCH 14, also a transport channel, and the DCH 14 is mapped to the DPDCH (Dedicated Physical Data Channel) 22.
The MAC-d sub-layer 24, as shown in FIG. 3, manages the DCH 14, the dedicated transport channel of a specific terminal. The MAC-e sub-layer 26 manages the E-DCH 16, the transport channel used for transmitting high-speed uplink data.
A MAC-d sub-layer of a transmitting side generates a MAC-d PDU (Protocol Data Unit) from a MAC-d SDU (Service Data Unit) received from an upper layer, namely, the RLC layer. Alternatively, a MAC-d sub-layer of a receiving side restores the MAC-d SDU from the MAC-d PDU received from a lower layer and delivers it to an upper layer. The MAC-d sub-layer may transmit the MAC-d PDU to the MAC-e sub-layer through a MAC-d flow, or transmit the MAC-d PDU to a physical layer through the DCH. The MAC-d sub-layer of the receiving side then restores the MAC-d SDU by using a MAC-d header included in the MAC-d PDU and then transfers the MAC-d SDU to the upper layer.
The MAC-e sub-layer of the transmitting side generates a MAC-e PDU from the MAC-d PDU, generated from the MAC-e SDU, received from the MAC-d sub-layer. Alternatively, the MAC-e sub-layer of the receiving side restores the MAC-e SDU from the MAC-e PDU received from the physical layer, and transfers it to an upper layer. In this case, the MAC-e sub-layer transmits the MAC-e PDU to the physical layer through the E-DCH. The MAC-e sub-layer of the receiving side then restores the MAC-e SDU by using a MAC-e header included in the MAC-e PDU and then transfers it to the upper layer.
A protocol model for a related art E-DCH is illustrated in FIG. 4. As shown, the MAC-e sub-layer supporting the E-DCH exists at a lower position of the MAC-d sub-layer of the UTRAN 26 and the terminal (UE) 28. The MAC-e sub-layer 30 of the UTRAN 26 is positioned in the Node B. The MAC-e sub-layer 32 exists in each terminal 28. Comparatively, the MAC-d sub-layer 34 of the UTRAN 26 is positioned in an SRNC for managing a corresponding terminal 28. Each terminal 28 includes a MAC-d sub-layer 36.
In the related art, when the uplink control information and the downlink control information for the E-DCH are transmitted through the physical control channel, the control information is to be transmitted according to a fixed format. This method requires the amount of control information transmitted at a time and transmission time to be uniformly set for every terminal and system. Thus, it is difficult to change the amount of uplink and downlink control information to be transmitted and the transmission time required for the E-DCH of the terminal. There is further a limitation on the Node B to dynamically control the data transmission through the E-DCH of the terminal. Therefore, it is difficult to add new uplink or downlink control information in line with future technical developments.